PROJECT SUMMARY: HIV-associated neurocognitive disorders (HAND) persists despite suppressive antiretroviral therapy (ART), in a mechanism likely involves myeloid cell activation. More reliable biomarkers and a better understanding of the pathophysiologic mechanisms driving HAND are needed to limit or halt the trajectory of this disorder. Recent advances in glycobiology have shown that glycan-lectin signaling plays critical roles in establishing several immune responses, including myeloid activation, and that glycan defects can underlie some neurological disorders. We asked whether an altered glycome might underlie HAND during ART. Using cutting-edge glycomic technologies, we found that plasma levels of a particular class of N-linked oligosaccharides ? un-sialylated ?(1,4) Gal GlcNAc (USG) ? were higher in HIV+ individuals on ART with cognitive impairment when compared to the un-impaired group. Further, greater levels of USG were associated with greater neurological impairment. Our group also has shown that plasma extracellular vesicles (EVs), key players in the body?s complex network of intercellular signaling, exert a pro-inflammatory effect on monocytes. The glycosylation features of EVs have been shown as a critical component to their functional activities. Together our data support the hypothesis that certain classes of circulating glycans may contribute to the pathogenesis and/or serve as biomarkers of HIV-associated cognitive impairment. We plan to investigate the role of cell-free glycans in the pathogenesis of HAND by leveraging a well-characterized clinical cohort of HIV+ individuals on ART with extensive clinical data, documented neuropsychological performance assessments, and brain magnetic resonance imaging (MRI) measurements. In Aim 1, we will assess the levels of circulating, cell-free glycans and EV-bound glycans in HIV+ individuals on suppressive ART, and define the relationship between these glycomic profiles and the degree of neurocognitive impairment in these individuals. An advanced high- density lectin microarray platform will be used to profile 96 different cell-free glycan structures in the plasma, and on purified EVs from these individuals. Glycan structures will be compared across the cognitive impairment spectrum defined through clinical diagnosis status, neuropsychological test performance scores, neuroinflammatory plasma measures, and MRI (brain metabolites and volumes). In Aim 2, we will determine the impact of cell-free glycan-lectin and EV-bound glycan-lectin interactions on peripheral monocyte activation and migration. Primary monocytes will be either enzymatically deglycosylated, depleting un-sialylated N-linked oligosaccharides, or treated with a specific carbohydrate-binding protein specific to it. Cells will then be exposed to EVs derived from impaired, or unimpaired HIV+ donors and effects will be measured on monocyte activation and migration. Our study will utilize the advent of new glycan-based technologies that can be harnessed to inform on mechanisms of HAND that may afford new diagnostics and/or treatment options for ameliorating cognitive impairment in this vulnerable population.